Should UseFunctionsWorkerDefaults() be included in the Aspire Azure Functions template?

[roend83]

I'm using AddAzureFunctionsProject with Aspire and the standard service defaults (AddServiceDefaults()). I wasn't seeing telemetry correlation between the Functions host process and the worker process in Application Insights -- traces appeared as separate, disconnected operations with no end-to-end distributed trace linking the host invocation to my function code.

After some digging, I found that adding UseFunctionsWorkerDefaults() from the Microsoft.Azure.Functions.Worker.OpenTelemetry package resolved this:

builder.AddServiceDefaults();
builder.Services.AddOpenTelemetry().UseFunctionsWorkerDefaults();
builder.ConfigureFunctionsWebApplication();

The Azure Functions OpenTelemetry documentation shows this call as required for .NET isolated worker apps. It:

• Correlates traces and logs between the host process and the worker process
• Configures a resource detector for Azure Functions
• Helps avoid duplicate telemetry between host and worker

Questions

1. Is this expected? Does AddServiceDefaults() intentionally not cover this, or is it an oversight that the Azure Functions template doesn't include it?
2. Should the Aspire Azure Functions project template include this call in the generated Program.cs? It seems like anyone using AddAzureFunctionsProject with Application Insights would hit this.
3. Should AddServiceDefaults() handle this automatically when it detects it's running in an Azure Functions worker? Or would that conflict with the host-level OpenTelemetry configuration?

What I observed without UseFunctionsWorkerDefaults()

• Host traces and worker traces had different operation IDs in Application Insights
• Distributed tracing across Service Bus triggers didn't connect the host invocation to the worker execution
• Log correlation between host and worker was missing

[davidfowl]

Should the Aspire Azure Functions project template include this call in the generated Program.cs? It seems like anyone using AddAzureFunctionsProject with Application Insights would hit this.

There's no such template.

I believe this is unresolved but documented on the functions side.

Agreed that something should be able to handle this, but there's no tooling detection on either side that understands a functions app is running. I think we'd need to work with the functions team to activate something in the core functions runtime if some configuraton were set from the apphost.

cc @fabiocav

[roend83]

I didn't see this anywhere in the documentation or in any of the samples I could find. Can you point me to where this is documented?